This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2001-063960, filed Mar. 7, 2001.
1. Field of the Invention
The present invention relates to a housing used for an electric apparatus, such as a portable computer, and more specifically, to such a structure that provides for thinner housings.
2. Description of the Related Art
An important factor for raising the commercial value of an electronic apparatus, such as a portable computer, is that it is compact and has excellent portability. Therefore, with regard to the housing enclosing various types of electronic devices, such as a hard disk drive device and a liquid crystal display panel, it is desired that the thickness of the housing be reduced as much as possible while maintaining the strength, rigidity and appearance of the apparatus.
In order to achieve the above, a magnesium alloy having a low relative density is conventionally used as the housing for portable computers. The conventional housing is made by a so-called thixo molding method, in which a magnesium alloy maintained at a half-melt state is injected into the molding space within a metal die. As compared to a housing made of synthetic resin, a magnesium-alloy equivalent can be formed with half or less the thickness of the synthetic resin. Accordingly, the overall weight of the housing can be reduced to that of an equivalent or less, in which a synthetic resin material is used.
In the case where a housing is formed by a thixo injection molding method, it is inevitable that as the thickness of the housing decreases, the mold space of the metal die is narrowed. Therefore, when injecting a magnesium alloy into the mold space, a high resistance is imparted to the magnesium alloy flowing in the mold space, and therefore the fluidity of the magnesium alloy is deteriorated.
In general, a magnesium alloy is injected into a mold space from one end thereof until it overflows from another end situated on the opposite side to the above one end, and thus the mold space is filled with the alloy. If the fluidity of the magnesium alloy within the mold space is poor, it is possible that the magnesium alloy cannot fully fill the entire mold space in the case of an A4-sized area, which is larger than, for example, a B5-sized area, even though no errors occur in a B5-sized area case in the mold space thereof. More specifically, magnesium alloy has a high thermal conductivity; therefore it is easily affected by the temperature of the metal die. Therefore, as the distance from one end of the mold space to the other end is increased due to the increase in the size of the mold space, the temperature of the magnesium alloy decreases as it reaches the other end of the mold space. As a result, the fluidity of the magnesium alloy is deteriorated at the other end of the mold space, thereby creating a magnesium-alloy unfilled region in this other end of the mold space.
Therefore, as the housing to be formed becomes thinner and larger in area, molding failures may frequently occur. As a result, the production yield is decreased, and the productivity and quality are adversely affected. At the same time, the production costs for the housing are undesirably increased.
The present invention has been achieved under the above-described circumstances, and the object thereof is to provide a high-quality housing, the productivity of which can be increased by suppressing the occurrence of mold errors and therefore the production cost of which is decreased.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.